1. Field of Invention
The present invention relates generally to the field of well bore zonal isolation tools and methods of using same in various oil and gas well operations.
2. Related Art
A zonal isolation tool should provide reliable, long-term isolation between two or more subsurface zones in a well. A typical application would be to segregate two zones in an open-hole region of a well, the zones being separated by a layer of low permeability shale in which the zonal isolation tool is placed. A nominal size configuration would be usable in wellbores drilled with an 8-½ inch (21.6 cm) outer diameter bit below 9-⅝ inch (24.5 cm) casing, but the use of zonal isolation tools is not limited to any particular size, or to use in open holes. By segregating open-hole intervals, downhole chokes may be used for production management. Similarly, selective zonal injection may be performed. If distributed temperature sensing is placed in the well, monitoring predictive control is possible.
A conventional completion assembly 10 with a zonal isolation tool 12 is illustrated in FIGS. 1 and 2 for allowing production of two separate flows 4A and 4B from an open hole 3. Assembly 10 may include a production packer 14, a gravel pack packer 16, flow control valves 18, and other components commonly used in downhole completions. Zonal isolation tool 12 may comprise a packer 20, a pair of anchors 22, a pair of polished bore receptacles (PBRs) 24, and an expansion joint 26. Service tools may include a setting string 28 and an isolation string 30.
Most of the current zonal isolation tools are made with an elastomeric membrane for sealing supported on a metallic support carriage structure for mechanical strength. In some constructions, the zonal isolation tools of this design may be composed of an inner sealing element, an integrated mechanical carriage structure, and an outer elastomeric element for sealing. The carriage can be made entirely of a composite material and thus integrates the mechanical support elements within a laminar structure of the composite body. Although these designs decrease extrusion of the inner elastomeric element through the carriage, further problems remain. One problem manifests itself in certain downhole conditions, for example at high temperatures, where the inner elastomeric element may be prone to extrusion through the support carriage structure when inflated. For support carriages having slats, the slats generally provide good protection against extrusion of the underlying elastomer through the slats, however, high friction coefficient between slats may make inflation/deflation difficult at high hydrostatic pressure.
Therefore, while there have been some improvements in zonal isolation tool design, further improvement is desired.